Westernport Water provides
water supply and
wastewater collection and
treatment services to an
area of 300km2 about 100km south east
of Melbourne, centred on the holiday
resort of Phillip Island. Although the
serviced area only has a resident
population of about 20,000, it experiences
peaks of over 100,000 persons during
events and holiday periods.
The Cowes wastewater treatment
plant, which was a conventional extended
aeration, activated sludge plant with
disinfected effluent discharge to Bass
Straight, was at full capacity. An analysis of
treatment options recommended modifying
the existing plant to biological nitrogen
removal (BNR) rather than constructing
a new plant. The upgrade involved
converting the extended aeration process
to BNR, while increasing the overall plant
capacity to handle projected influent loads
up to 2021. The major changes involved:
l Incorporating an anoxic zone for
biological denitrification;
l An internal mixed liquor recycle of
up to twice the average daily flow;
l Peak wet weather loading is to be
handled by a new storm bypass
system to protect the biological
process to an enlarged storm
storage facility.
To provide increased capacity,
upgrades were made to:
l the inlet works
l bioreactor
l internal pumping station
l sludge digester, and
l sludge drying systems.
The major challenge was to provide
continuous operation of the plant within
the licence limits during construction. This
was managed by careful scheduling of
construction activities to select the
best timing and duration of individual
work components.
In summary, the upgrade was
complex and challenging, but it was
completed on time and within budget
with no breaches of the licence effluent
limits. The upgrade was completed in
June 2015 and since commissioning
of the anoxic tank effluent quality has
improved despite increases in inflow
volumes. A comparison of the effluent
quality before and after conversion is
given in the table below.
To read the full article, visit the
Water e-Journal at bit.ly/e-Journal
LICENCE LIMIT
PLANT EFFLUENT
Compliance
Period
Effluent
Discharge
Licence Limit
2014 -
Jun 2015 July-
Sept
2015
Mean daily discharge Year (median) 4ML/day
2.7
3.2
Max discharge
Month (max) 8.6ML/day
8.5
8.4
BOD5
Year (median) 5mg/L
5
3
SS
Year (median) 10mg/L
4
5
Ammonia as N
Year (median) 5mg/L
0.4
0.2
Total N
Year (median) 45mg/L
28
14
Total P
Year (median) 15mg/L
8.9
7.1
E. Coli
Year (median) 200 org/100ml 0
1
pH
Monthly range 6-9
6.5
7.4
Anionic surfactants Month (max) 1mg/L
0.09
0.08
Total residual
chlorine
Month (max) 1mg/L
0.78
0.75
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